This relates to bicycles, and more particularly to foot pedal crank arm constructions for bicycles. According to the invention, the foot pedal crank arms include crank arm extensions that move radially in and out along the lengths of the associated crank arms so as to effectively vary the crank arm length during each crank arm revolution. During the power stroke (downstroke) the crank arm is made to be relatively long; during the return stroke (upstroke) the crank arm is made to be relatively short. Change in crank arm length is achieved automatically without any special effort on the part of the bicyclist.
By increasing and then decreasing the crank arm length during each crank arm revolution it is estimated that increased leverage can be obtained without increasing pedal travel circumference or without adversely affecting bicyclist comfort and leg action. It is believed that the rider can produce about eight percent more power or speed when using the invention, compared to conventional bicycles.
U.S. Pat. No. 550,206 to Tompkins shows a bicycle having pedal crank arms whose lengths automatically increase and decrease during each crank arm revolution. The sliding surfaces within the crank arms are flat frictional surfaces that consume substantial amounts of energy, thereby negating some of the benefits that would otherwise be achieved by the variable length crank arm feature. The present invention is an improvement on the system shown in U.S. Pat. No. 550,206. Under the present invention anti-friction roller components are incorporated into the crank arms in an effort to materially reduce the friction losses associated with flat friction surface engagements of the type present in the structure of U.S. Pat. No. 550,206.
The principal aim of the present invention is to improve the operating efficiency of the variable length crank arm construction shown in U.S. Pat. No. 550,206. A further aim of the invention is to provide a variable length crank arm construction that is relatively sturdy while being manufacturable at relatively low cost.